In order to get started, you'll want to install Grunt's command line interface (CLI) globally. You may need to use sudo (for OSX, *nix, BSD etc) or run your command shell as Administrator (for Windows) to do this.

npm install -g grunt-cli

This will put the grunt command in your system path, allowing it to be run from any directory.

Note that installing grunt-cli does not install the Grunt task runner! The job of the Grunt CLI is simple: run the version of Grunt which has been installed next to a Gruntfile.
This allows multiple versions of Grunt to be installed on the same machine simultaneously.

Each time grunt is run, it looks for a locally installed Grunt using node's require() system. Because of this, you can run grunt from any subfolder in your project.

If a locally installed Grunt is found, the CLI loads the local installation of the Grunt library, applies the configuration from your Gruntfile, and executes any tasks you've requested for it to run. To really understand what is happening, read the code.

A typical setup will involve adding two files to your project: package.json and the Gruntfile.

package.json: This file is used by npm to store metadata for projects published as npm modules. You will list grunt and the Grunt plugins your project needs as devDependencies in this file.

Gruntfile: This file is named Gruntfile.js or Gruntfile.coffee and is used to configure or define tasks and load Grunt plugins.
When this documentation mentions a Gruntfile it is talking about a file, which is either a Gruntfile.js or a Gruntfile.coffee.

The package.json file belongs in the root directory of your project, next to the Gruntfile, and should be committed with your project source. Running npm install in the same folder as a package.json file will install the correct version of each dependency listed therein.

There are a few ways to create a package.json file for your project:

Most grunt-init templates will automatically create a project-specific package.json file.

The easiest way to add Grunt and gruntplugins to an existing package.json is with the command npm install <module> --save-dev. Not only will this install <module> locally, but it will automatically be added to the devDependencies section, using a tilde version range.

For example, this will install the latest version of Grunt in your project folder, adding it to your devDependencies:

npm install grunt --save-dev

The same can be done for gruntplugins and other node modules. As seen in the following example installing the JSHint task module:

npm install grunt-contrib-jshint --save-dev

Checkout the current available gruntplugins to be installed and used on your project at the plugins page.

Be sure to commit the updated package.json file with your project when you're done!

The Gruntfile.js or Gruntfile.coffee file is a valid JavaScript or CoffeeScript file that belongs in the root directory of your project, next to the package.json file, and should be committed with your project source.

In the following Gruntfile, project metadata is imported into the Grunt config from the project's package.json file and the grunt-contrib-uglify plugin's uglify task is configured to minify a source file and generate a banner comment dynamically using that metadata. When grunt is run on the command line, the uglify task will be run by default.

Most Grunt tasks rely on configuration data defined in an object passed to the grunt.initConfig method.

In this example, grunt.file.readJSON('package.json') imports the JSON metadata stored in package.json into the grunt config. Because <% %> template strings may reference any config properties, configuration data like filepaths and file lists may be specified this way to reduce repetition.

You may store any arbitrary data inside of the configuration object, and as long as it doesn't conflict with properties your tasks require, it will be otherwise ignored. Also, because this is JavaScript, you're not limited to JSON; you may use any valid JS here. You can even programmatically generate the configuration if necessary.

Like most tasks, the grunt-contrib-uglify plugin's uglify task expects its configuration to be specified in a property of the same name. Here, the banner option is specified, along with a single uglify target named build that minifies a single source file to a single destination file.

Many commonly used tasks like concatenation, minification and linting are available as grunt plugins. As long as a plugin is specified in package.json as a dependency, and has been installed via npm install, it may be enabled inside your Gruntfile with a simple command:

// Load the plugin that provides the "uglify" task.
grunt.loadNpmTasks('grunt-contrib-uglify');

You can configure Grunt to run one or more tasks by default by defining a default task. In the following example, running grunt at the command line without specifying a task will run the uglify task. This is functionally the same as explicitly running grunt uglify or even grunt default. Any number of tasks (with or without arguments) may be specified in the array.

// Default task(s).
grunt.registerTask('default', ['uglify']);

If your project requires tasks not provided by a Grunt plugin, you may define custom tasks right inside the Gruntfile. For example, this Gruntfile defines a completely custom default task that doesn't even utilize task configuration:

The Installing grunt guide has detailed information about installing specific, production or in-development, versions of Grunt and grunt-cli.

The Configuring Tasks guide has an in-depth explanation on how to configure tasks, targets, options and files inside the Gruntfile, along with an explanation of templates, globbing patterns and importing external data.

The Creating Tasks guide lists the differences between the types of Grunt tasks and shows a number of sample tasks and configurations.